Street lighting luminaires generate light patterns that may be evaluated in a classification system known as BUG, for Backlight, Uplight and Glare. BUG is a reference tool, and other metrics may exist to characterized street light performance with respect to an angular altitude direction from vertical down, where upward pointing light has a direction angle from 90° up to 180°, and whether light is directed toward an intended area of illumination or outside at altitude angles from 0° to 90°, as well as azimuth direction in a horizontal plane.
Glare may be generally termed as downward directed light pointing in the intended illumination direction but which may also produce annoying or visually disabling levels of light. Backlight creates generally downward pointing light trespassing onto adjacent sites that may be illuminated by other luminaires, or is altogether undesirable illumination. To a certain extent, Backlight is wasteful and/or undesirable. Uplight is undesirable artificial skyglow, which may adversely affect astronomy with backscattered light pollution, and is mostly wasted energy. Control of the beam pattern and intensity produced by a luminaire may depend at least on the type of light source selected, focusing and redirection of emitted light, including, but not limited to, the use of reflectors, optical correction (e.g., lenses), and shielding (e.g., chimney- or tunnel-type restrictors).
One type of light source is a light emitting diode (LED), which may typically produce satisfactory levels of light intensity at power levels lower than may be needed for incandescent, vapor glow or other light sources. A light emitting diode comprises a semiconductor material impregnated, or doped, with impurities. These impurities add “electrons” and “holes” to the semiconductor, which can move in the material relatively freely. Depending on the kind of impurity, a doped region of the semiconductor can have predominantly electrons or holes, and is referred to as an n-type or p-type semiconductor region, respectively.
In LED applications, an LED semiconductor chip includes an n-type semiconductor region and a p-type semiconductor region. A reverse electric field is created at the junction between the two regions, which causes the electrons and holes to move away from the junction to form an active region. When a forward voltage sufficient to overcome the reverse electric field is applied across the p-n junction, electrons and holes are forced into the active region and combine. When electrons combine with holes, they fall to lower energy levels and release energy in the form of light. The ability of LED semiconductors to emit light has allowed these semiconductors to be used in a variety of lighting devices. For example, LED semiconductors may be used in general lighting devices for interior applications or in various exterior applications.
During manufacture, an array comprising a large number of LED semiconductor devices (or dies) are produced on a substrate. Chip-on-board (COB) lights include multiple LED chips packaged together as one lighting module forming a large effective emitting surface, giving the appearance of an “extended” light source. In comparison to a single die (i.e., single chip) LED, which approximates a point source, it is more difficult to design optical lenses for use with large COB LEDs to control the illumination light pattern projected for street lighting to avoid undesirable glare, backlight and uplight. It may be generally desirable to limit glare, for example, beyond 60°-70°, and somewhat similarly for backlight, so as to avoid undesirable illumination, such as may be directed toward residential windows
Accordingly, what is needed is a lens design for COB LEDs that form highly efficient optical beam patterns for various applications including street lighting that limit light pollution.